Regular Expression Denial of Service

Overview

In websocket-extensions before version 0.1.4, there is a vulnerability which allows an attacker to exhaust the server’s capacity to process
incoming requests by sending a WebSocket handshake request containing a header
of the following form:

`Sec-WebSocket-Extensions: a; b="\c\c\c\c\c\c\c\c\c\c ...`

That is, a header containing an unclosed string parameter value whose content is
a repeating two-byte sequence of a backslash and some other character. The
parser takes exponential time to reject this header as invalid, and this will
block the processing of any other work on the same thread. Thus if you are
running a single-threaded server, such a request can render your service
completely unavailable.

Recommendation

Upgrade to version 0.1.4 or later

References

• CVE
• GitHub Advisory